1. The Field of the Invention
The subject matter of the present invention is a method of making a coated three-dimensionally shaped glass ceramic body and, especially a method of making a coated three-dimensionally shaped glass ceramic window pane for a fireplace or oven viewing window.
2. Related Art
Glass ceramic panels or plates are used, above all, as window panes and are generally made in one piece. Not only can they be flat, but also they can be three-dimensionally shaped, for example, angled, bulged, and also they can have a shape that is a mixture of different forms. Three-dimensionally shaped glass ceramic panels are made by bending or curving a green glass body and subsequently ceramizing it. It is sometimes even possible to simultaneously ceramize and shape the green glass body with simple shaping techniques. A glass ceramic body is made in a known way in which a green glass body, which has a composition suitable for conversion into a glass ceramic body, is subjected to a ceramizing process. The ceramizing process comprises first heating the glass at a temperature at which crystal nuclei form and subsequently at a higher temperature to perform the ceramizing with the help of the already formed crystal nuclei in the ceramizing step.
The resulting glass ceramic is especially resistant to heating and temperature changes, which makes it especially suitable for many applications, especially viewing window panes.
Glass ceramic plates or panels are used in the lighting industry as window panes for powerful light sources, window panes in space heaters, oven door or baking oven window panes, cook tops for stoves and in many other applications, in which good mechanical strength and temperature change resistance are required.
Currently glass ceramic panels are increasingly used as window panes in fireplace applications, in which the spreading of sparks and glowing embers into the living area is prevented by means of a transparent window pane. The window pane allows observation of the flames. Also a viewing window pane is frequently built into a fireplace oven in order to permit observation of the fire and/or the embers. It is possible to build the viewing window pane into a door frame, e.g. a metal door frame, or to use the viewing window pane directly as a door or window for closure of the space in which the fire is contained.
In many cases for aesthetic reasons the glass ceramic window pane is provided with a reflective coating after it has been made, so that one can of course see the flames and/or the light when the light source, the fireplace or the oven is operated, but not the space behind the window pane, i.e. the unattractive interior structure of the oven or fireplace, which remains dark, when the light source is turned off or the fire is put out, as described for example in US Published Patent Application 2006/0024509 A1.
The glass ceramic is coated according to the usual methods, especially by pyrolysis of powder, liquid or gas, by vapor deposition or by sputtering, particularly by plasma-assisted deposition methods and reactive sputtering of a suitable metal in the presence of oxygen and/or nitrogen and the like.
The coating that is applied can be a single-layer coating, e.g. ITO for reflection of IR radiation, or a multi-layer coating, e.g. an interference layer system of several high and low refractive index layers, which each have a layer thickness in the vicinity of about a quarter of the average wavelength of light, so that the observed color of the coated glass ceramic is from a blue-silver to golden depending on the structure and layer thickness. The layer system should be scratch-resistant, so that it can be cleaned without damaging it. Soft layers are preferably protected from scratches with hard covering-layers.
While the coating of a flat glass ceramic window pane is relatively easy and can be performed with a conventional coating apparatus for flat glass, the coating of a three-dimensionally shaped glass ceramic window pane is substantially more difficult, since the geometry of the coating apparatus must be adjusted for each shape to provide a uniform coating.